The present invention relates generally to a system including an arrangement for tracking the positional relationship between a boring tool and one or more buried lines such as, for example, pipes, cables, conduits or other conductors and more particularly to an arrangement for indicating certain changes in the positional relationship between the boring tool and the lines based upon a particular characteristic of a magnetic field emanated from the boring tool or a magnetic field emanated from each one of the lines. In one aspect of the invention, an arrangement and associated method are provided for tracking the positional relationship between a boring tool and one or more buried lines using a composite magnetic signal.
The installation of utility lines underground is increasingly popular for reasons of aesthetics and for practical reasons such as, for example, protecting these lines from the effects of severe above ground weather conditions. However, in areas where buried lines have previously been installed, it is undesirable to excavate an entire pathway for the purpose of installing additional lines since such excavation many times results in the unintentional damage of an existing utility line. Areas which include buried fiber optic cables are particularly problematic for several reasons. First, a fiber optic cable is extremely difficult to repair once it has been severed or damaged. Second, because a fiber optic cable is capable of simultaneously carrying a vast amount of information, downtime can be quite costly.
In the past, various horizontal boring tool locating and monitoring systems have been developed which advantageously eliminate the need for excavating the entire pathway in which a utility line is to be installed. One such system is described in U.S. Pat. No. 5,337,002 (issued to the inventor of the present invention) which is incorporated herein by reference. FIG. 1 is taken directly from the '002 patent and illustrates a horizontal boring operation being performed by an apparatus which is generally designated by the reference numeral 10. Boring apparatus 10 includes a drill head 12 incorporating a transmitter which transmits a locating signal 14. A portable hand held receiver (locator) 16 is used to detect the locating signal through the intervening earth whereby to ultimately guide the boring tool to a terminating pit 18. The system relies on its operator having prior knowledge of any obstacles in the boring path of the tool such as an obstacle 20 so that the tool can be steered around the obstacle. Unfortunately, such prior knowledge may be inaccurate, if available at all. Moreover, the system of FIG. 1 does not by itself provide a direct indication of the relationship between a respective obstacle such as an in-ground line and the boring tool. Without this indication, the operator is in danger of possibly damaging an in-ground line with no forewarning. In view of the serious consequences of damaging certain buried lines, as described above, operators of boring tools are less and less willing to assume this risk.
As will be seen hereinafter, the present invention provides a highly advantageous arrangement and associated method for providing an operator with indications which warn the operator when a boring tool is approaching an in-ground obstacle such as a fiber optic cable. Dependent upon the specific indications provided to the operator, an appropriate course of action may thereafter be taken which assures that the boring tool will not damage the line. In another advantage, the present invention provides an arrangement which utilizes a composite magnetic signal in determining both the directional heading of the boring tool and the positional relationship between the boring tool and the underground line(s). The arrangement may be configured so as to enable simultaneous tracking of the positional relationship between the boring tool and a plurality of in-ground lines whereby to avoid physical contact of the boring tool with the lines.